J3/06-329r1

Date:    16 November 2006
To:      J3
From:    Aleksandar Donev
Subject: Clarifications for SYNC ALL/IMAGES and QUERY
References: 06-007r1, resubmit of 06-286r1
Dependencies: None

Following some comments from Van and discussion in subgroup B, I
propose clarifications of text concerning SYNC IMAGES and QUERY.
No technical change is made, merely clarifications.

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Note 8.38 does not explain if there is a difference between
SYNC IMAGES(*) being executed on all images and SYNC_ALL. Here is an
attempt to make it more informative and clarify the reason for having
both SYNC IMAGES(*) and SYNC ALL:

[199:15+] In Note 8.38, replace the first three sentences with:
"Execution of SYNC IMAGES (*) on all images has the same effect as
execution of SYNC ALL on all images, but SYNC ALL might have better
performance. SYNC IMAGES statements are not required to specify the
entire image set, or even the same image set, on all images
participating in the synchronization."

Then split off "In the following example" as a separate paragraph.

-------------------
The text describing QUERY and when it is satisfied etc. is very
difficult to understand. This is an attempt to rewrite it:

[200:9-201:4] Replace the three paragraphs with:

A QUERY statement is <<blocking>> if and only if it has no READY=
specifier. A QUERY statement is <<satisfied>> on completion of its
execution if and only if it is a blocking QUERY statement or it set
the variable specified by its READY= specifier to true. Let Q_{M<-T}
denote the number of times image M has completed the execution of a
satisfied QUERY statement with a different image T in its image set.

Completion of execution on image M of a blocking QUERY statement is
delayed until, for each different T in its image set,
N_{T->M} > Q_{M<-T}.

During the execution on image M of a non-blocking QUERY statement, the
<scalar-logical-variable> becomes defined. The value becomes false if,
for a different image T in the image set, N_{T->M} <= Q_{M<-T}.
Otherwise, the value becomes true.